Did a x5 with 2 friends, they were alliance I was horde. Everything seemed fine, we all had the same score (335) and entered at the same time (within a couple seconds)
But look at what they got compared to what I got, and to confirm I double checked my items, and yep, I had infact used 5, from 9 to 4.
imgur. com/o0TEHiI.png
I contacted support and they told me to post on here.